Water based metal-working fluids (MWF) and their microbial contaminants are associated with respiratory symptoms, acute changes in lung function, occupational asthma, and hypersensitivity pneumonitis. The National Institute for Occupational Safety and Health (NIOSH) recently found compelling evidence of respiratory health effects, and proposed lowering the recommended exposure limit for MWF 10 fold to 0.5 mg/m3 of total aerosol. NIOSH proposed regulations based on gravimetric measurements alone, even though there is mounting evidence that microbiologic factors, particularly endotoxin, play significant causal roles in the effects of MWF on airways, and that fungi, mycobacteria and gram-positive bacteria in MWF are the cause of hypersensitivity pneumonitis outbreaks. The lack of well established methods and the small number of epidemiologic studies using measures of microbiologic exposure prompted this omission. Yet, failure to regulate microbial exposure may result in insignificant health effects even when gravimetric levels meet the new standard. Therefore, this project will fill the research gap in methods to assess exposure to mixtures (a NORA priority) of microbial agents. In the first year, the investigators will adapt and validate chemical markers which the investigators previously developed for fungi, mycobacteria, Legionella species, pepitoglycan, and lipopolysaccharide; validate PCR methods for use with MWFs; and validate endotoxin measurements in MWF aerosols. In the following year, the investigators will use these methods in a large field study at General Motors. The investigators will study 15 automotive machining operations (5 each) using soluble, semi-synthetic and synthetic MWFs, in 10 to 15 different plants. In each of the 15 machining areas, and in control areas in the same plants, the investigators will measure gravimetric and microbiologic exposures. With this data the investigators will test hypotheses about the suitability and improved utility of the new biomarkers relative to traditional culture based methods of exposure assessment. The investigators will also test the hypothesis that the relationship between total MWF aerosol and airborne endotoxin varies from plant-to-plant, so that endotoxin measurements provide independent information about exposure to respiratory hazards in the machining environment. This study will be among the largest exposure assessment studies of MWF, including up to 15 plants, rather than focus on one or two plants, and it will be the first large survey of MWF exposure to incorporate state-of-the-art microbial biomarkers. The data obtained may well play an important role in the Federal rule-making process.